1. Field of the Invention
The present invention relates to a driving control apparatus that executes driving control of a vehicle by selecting a vehicle that is traveling in front of the vehicle so that it can follow that vehicle. More specifically, the present invention relates to a driving control apparatus that executes a low speed following (LSF) in which the vehicle can be started or stopped following the preceding vehicle in a relatively low vehicle speed region.
Priority is claimed on Japanese Patent Application No. 2004-320401, filed Nov. 4, 2004 and Japanese Patent Application No. 2005-298563, filed Oct. 13, 2005, the contents of which is incorporated herein by reference.
2. Description of the Related Art
In recent years, various types of driving control apparatuses have been developed which are aimed at reducing the driver's work load in operating the vehicle.
One type of such apparatuses is a driving control apparatus that executes a low-speed follow-up control that controls a driving state of a vehicle such that a predetermined inter-vehicle distance is maintained between the vehicle and a preceding vehicle when the vehicle is traveling at a low speed (including when the vehicle is stopped).
For example, Japanese Patent No. 3194305 discloses a technique in which when a vehicle is stopped at the front at a red light at an intersection or at the front at a railroad crossing, if a brake pedal is depressed and the vehicle speed is zero, the stopped state is maintained by a brake operating device. With this technique, even when the inter-vehicle distance to the preceding vehicle is increased, the brake hold state is not canceled. The brake hold state is canceled when the inter-vehicle distance to the preceding vehicle is equal to or less than a predetermined value and when a relative speed with respect to the preceding vehicle is a positive value.
Millimeter-wave radar apparatuses are widely used as devices for detecting a preceding vehicle. However, these radar apparatuses may fail to detect an object which is at a shorter distance than the detectable distance since the time interval between the time when the radar transmits electromagnetic waves and the time when the waves reflected by the object are received is short. Therefore, even when a vehicle is preceding the vehicle, the LSF control is not executed since the preceding vehicle is not detected when the distance from the preceding vehicle is very short, or when a pedestrian passes between the vehicles, for example. As a result, the driver is required to operate the brake manually and continuously in order to maintain the vehicle in the stopped state, which is an inconvenience to the driver. In addition, the driver may feel discomfort since a follow-up control is cancelled even when the vehicle is preceding the vehicle.
Accordingly, the present invention is directed to provide a driving control apparatus that is capable of continuing an execution of an LSF control even when no preceding vehicle is detected in order to enhance the convenience without discomforting the driver.